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Intimations of Imminent Global Cooling
Reference
Bratcher, A.J. and Giese, B.S. 2002. Tropical Pacific decadal variability and global warming. Geophysical Research Letters 29: 10.1029/2002GL015191.

Background
The authors note that the general trend of global surface air temperature over the past century or so is one of warming, but that there is "considerable variation in the upward trend." They also correctly note that "how much of this variability is attributable to natural variations and how much is due to anthropogenic contributions to atmospheric greenhouse gases has not yet been resolved," stating that "the possibility exists that some portion of the recent increase in global surface air temperature is part of a naturally oscillating system."

What was done
In the words of the authors, their paper "explores the recent record of Southern Hemisphere subsurface temperature anomalies and whether they may be an indicator of future global surface air temperature trends."

What was learned
Bratcher and Giese report that "low frequency changes of tropical Pacific temperature lead global surface air temperature changes by about 4 years" and that "anomalies of tropical Pacific surface temperature are in turn preceded by subsurface temperature anomalies in the southern tropical Pacific by approximately 7 years." They also document a distinct cooling of the southern tropical Pacific over the last 8 years, leading them to conclude that ...

What it means
... "the warming trend in global surface air temperature observed since the late 1970s may soon weaken." Indeed, they report that "conditions present in the southern tropical Pacific resemble those prior to the 1976 climate shift [after which the temperature of the region rose by a full 1C], except with the opposite sign [our italics]," stating that "a climate shift to pre-1976 conditions could lessen the warming trend that has existed since 1976." For more on this possibility, which could actually lead to global cooling, see our Journal Reviews Cooling on the Horizon? and Nutrient-Rich Subarctic Water Invades California Current.

On another note, the authors say their results "do not preclude the possibility that anthropogenic sources of greenhouse gases have contributed to global warming." However, they feel that they "do indicate that the human forced portion of global warming may be less than previously described."


Reviewed 14 May 2003